1. Field of the Invention
The present invention relates generally to a rear suspension system for motorcycles. More particularly, the invention relates to a rear suspension system for motorcycles which provides a progressive damping characteristic in response to up and down movements of a rear wheel of the motorcycle.
2. Description of Relevant Art
In a known conventional rear suspension system for motorcycles, a damping force of a shock absorber is relatively small within a range of relatively small rocking motion of a rear wheel supporting member and is relatively large within a range of relatively large rocking motion of the rear wheel supporting member. The rear wheel supporting member of such known rear suspension system has a rear wheel supported at a rear end thereof and is mounted at a forward end thereof for up and down rocking motion on a motorcycle body frame. One end of a link is pivotally mounted on the rear wheel supporting member while one end of another link is pivotally mounted on the body frame. The opposite ends of the two links are connected to each other, and a shock absorber having one end thereof connected to the body frame is connected at the other end thereof to either one of the two links.
According to such known rear suspension system, the damping force or the magnitude of compression of the shock absorber when the rear wheel supporting member is rocked upwardly to permit upward movements of the rear wheel in following undulations of a road surface, increases curvilinearly relative to a stroke of rocking motion of the rear wheel supporting member due to restricting actions of the two links upon the body frame, thereby providing a progressive damping force characteristic.
In such a conventional rear suspension system for motorcycles, the rear wheel supporting member must have a substantial weight in order for it to be sufficiently strong to bear a gradually increasing damping force, and accordingly the unsprung load of the motorcycle must undesirably be relatively large when compared with a rear suspension system which does not provide a progressive damping characteristic, thus requiring that a shock absorber having a large capacity and hence a great load be provided. In order to alleviate such situation, the degree of a progressive change of the damping force must be made relatively small.
The present invention effectively overcomes the foregoing problems attendant conventional rear suspension systems for motorcycles.